<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        function show(){
            alert('a');
        }
       // setInterval(show,1000);  //无限执行下去
        setTimeout(show,1000);  //只执行一次

    </script>
</head>
<body>

</body>
</html>